Aqueous uretdione group-containing compositions and method for producing same

ABSTRACT

The invention relates to aqueous uretdione group-containing compositions comprising or consisting of (A) at least one uretdione group-containing curing agent based on aliphatic, cycloaliphatic, araliphatic, and/or aromatic polyisocyanates which do not contain chemically bonded hydrophilating groups; (B) at least one hydroxy group-containing polyol which contains at least one chemically bonded carboxylic acid group; (C) optionally solvents; and (D) optionally auxiliary agents and additives; wherein the quantity ratio of the components (A) and (B) is measured such that the molar ratio of the NCO groups of the curing agent (A), said groups being provided in the form of uretdione, to the NCO reactive groups of the polyol (B) equals 3.0:0.5 to 0.5:3.0, and A and B are provided as a physical mixture. The invention additionally relates to a method for producing a polyurethane layer using the aqueous uretdione group-containing composition according to the invention, to the polyurethane layer obtained therefrom, and to a substrate which is coated with or adhered to the polyurethane layer.

The present invention relates to aqueous uretdione group-containing compositions comprising or consisting of

-   (A) at least one uretdione group-containing curing agent based on     aliphatic, cycloaliphatic, araliphatic and/or aromatic     polyisocyanates that contains no chemically-bonded hydrophilizing     groups; -   (B) at least one hydroxyl-containing polyol that contains at least     one chemically-bonded carboxylic acid group; -   (C) optionally solvents; and -   (D) optionally auxiliaries and additives;     -   wherein the quantitative ratio of components (A) and (B) is such         that the molar ratio of the NCO groups of the curing agent (A)         present as uretdione to NCO-reactive groups of the polyol (B) is         3:0.5 to 0.5:3 and wherein A and B are present as a physical         mixture.

The invention further relates to a process for producing a polyurethane layer using the aqueous uretdione group-containing composition of the present invention, to the polyurethane layer obtained therefrom, and to a substrate that is coated or bonded with said polyurethane layer.

Recent years have seen a sharp rise in the profile of aqueous paints and coating compositions in the wake of increasingly stringent emissions directives governing the solvents given off when applying paints. Although for many fields of application there are now aqueous coating systems available, these systems are often unable to attain the high quality level of conventional, solvent-based paints in respect of resistance to solvents and chemicals or elasticity and mechanical durability. In particular, there has been no disclosure to date of any polyurethane-based coating compositions that can be processed from an aqueous phase and that go far enough towards satisfying the exacting requirements of the art. This statement applies both to DE 4001783 A1, which relates to special anionically modified aliphatic polyisocyanates, and to the systems of DE 2456469 A1, DE 2814815 A1, EP 0012348 A1, and EP 0424697 A1, which describe aqueous, one-component baking-enamel binders based on blocked polyisocyanates and organic polyhydroxy compounds.

In recent years, further improvements to one-component baking-enamel binders based on blocked polyisocyanates have been achieved, as described for example in EP 0576952A.

The above one-component baking-enamel binders of the prior art that are based on blocked polyisocyanates have the disadvantage, even if they are largely solvent-free, that the blocking agents are released when the enamel binders are baked, which in turn contributes to emissions.

There has consequently long been a market demand for developing aqueous, emission-free one-component baking-enamel binders. There has been no shortage of attempts at producing such baking-enamel binders based on uretdione-containing polyisocyanates that do not give rise to elimination products.

According to EP 1687354 A1, aqueous uretdione-containing dispersion coatings can be produced by combining a solid uretdione compound with a molten water-dispersible resin, salting the water-dispersible resin if necessary, and dispersing the resin mixture in water. The molten water-dispersible resin may contain a functionality that is reactive toward the uretdione compound, or the coating composition may contain another water-dispersible resin having a functionality that is reactive toward the uretdione compound. In the example, an epoxy resin was however used. Epoxy coatings are generally known to be inferior in most properties to polyurethane coatings. According to EP 1687354 A1, it is also necessary to use an additional emulsifier in the production of these dispersion coatings, which further compromises the coating properties of the dispersion coatings. In addition, the method of production described in EP 1687354 A1 is associated with very high thermal stress on the uretdione groups, which in practice would most likely lead to loss of the uretdione groups. The dispersions described in EP 1687354 A1 were moreover applied immediately, directly after preparation. EP 1687354 A1 provides no information on the stability of these dispersions.

U.S. Pat. No. 4,496,684 A described uretdione group-containing polyurethane oligomers prepared by reacting a hydroxyl-terminated prepolymer with a dicarboxylic anhydride. This document does not include any aqueous composition in which the uretdione group-containing curing agent and the polyol are present as a physical mixture.

Further examples of water-dispersible hydrophilic uretdione-containing polyisocyanates are given in, for example, DE 2538484 A1 and DE 10 2005 036 654 A1. In both documents, a hydrophilizing group (i.e. a carboxyl group) was incorporated directly into the uretdione-containing polyisocyanate. Neither DE 2538484 A nor DE 10 2005 036 654 A1 give any information on the stability of these dispersions. These also differ in that no physical mixtures of a specific uretdione group-containing curing agent and a specific polyol are present.

US 2015232609A1 discloses water-dispersible hydrophilic uretdione-containing polyisocyanates obtainable by reacting a prepolymer bearing uretdione groups with an emulsifier containing an ionogenic group, with the ionogenic group having either a pKa of >8 or a pKb of >8 in water at room temperature. Although such uretdione-containing reaction products exhibited an improved storage stability of 8 weeks at room temperature, this is still inadequate for practical uses in industry, where it is not uncommon for transport over long distances to be necessary.

The above problems were surprisingly solved by using a physical mixture of the specific curing agent and the specific polyol of the present invention. In particular, dispersions were obtained that show increased storage stability compared to known prior art compositions.

The present invention relates in particular to:

-   1. Aqueous uretdione group-containing compositions comprising or     consisting of -   (A) at least one uretdione group-containing curing agent based on     aliphatic, cycloaliphatic, araliphatic and/or aromatic     polyisocyanates, preferably based on based on aliphatic,     cycloaliphatic and/or araliphatic polyisocyanates, more preferably     based on aliphatic and/or cycloaliphatic polyisocyanates, that     contains no chemically-bonded hydrophilizing groups; -   (B) at least one hydroxyl-containing polyol that contains at least     one chemically-bonded carboxylic acid group; -   (C) optionally solvents; and -   (D) optionally auxiliaries and additives;     -   wherein the quantitative ratio of components (A) and (B) is such         that the molar ratio of the NCO groups of the curing agent (A)         present as uretdione to NCO-reactive groups of the polyol (B) is         3.0:0.5 to 0.5:3.0, preferably 2.5:1.0 to 1.0:2.5, more         preferably 2.0:2.0 to 1.0 to 1.0:2.0, and wherein (A) and (B)         are present as a physical mixture. -   2. Aqueous uretdione group-containing composition according to     aspect 1, characterized in that the at least one uretdione     group-containing curing agent (A) was obtained by reacting monomeric     isocyanates comprising or consisting of at least one monomeric     isocyanate selected from tetramethylene diisocyanate,     cyclohexane-1,3-diisocyanate and cyclohexane-1,4-diisocyanate,     pentamethylene diisocyanate, hexamethylene diisocyanate (HDI),     1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane     (isophorone diisocyanate IPDI),     dicyclohexylmethane-2,4′-diisocyanate and/or     dicyclohexylmethane-4,4′-diisocyanate, tetramethylxylylene     diisocyanate (TMXDI), triisocyanatononane, tolylene diisocyanate     (TDI), diphenylmethane-2,4′-diisocyanate and/or     diphenylmethane-4,4′-diisocyanate (MDI),     triphenylmethane-4,4′-diisocyanate or naphthylene-1,5-diisocyanate     or mixtures thereof, preferably from isophorone diisocyanate,     dicyclohexylmethane-2,4′-diisocyanate and/or     dicyclohexylmethane-4,4′-diisocyanate, or hexamethylene     diisocyanate. -   3. Aqueous uretdione group-containing composition according to     aspect 1 or 2, characterized in that     -   hydroxyl-containing monomers and/or polymers are used as         starting materials for the at least one uretdione         group-containing curing agent (A). -   4. Aqueous uretdione group-containing composition according to any     of the preceding aspects, characterized in that     -   the at least one uretdione group-containing curing agent (A) has         a free NCO content of less than 5% by weight and a content of         uretdione groups of 1% to 18% by weight (calculated as C₂N₂O₂,         molecular weight 84 g/mol). -   5. Aqueous uretdione group-containing composition according to any     of the preceding aspects, characterized in that     -   the aqueous composition has an acid value of 1 to 100 mg KOH/g,         preferably 2 to 50 mg KOH/g, more preferably 5 to 30 mg KOH/g,         preferably measured in accordance with DIN EN ISO 2114: 2002-06         with acetone and ethanol in a weight ratio of 2:1 as solvent,         and calculated based on the solids content. -   6. Aqueous uretdione group-containing composition according to any     of the preceding aspects, characterized in that     -   the at least one hydroxyl-containing polyol (B) was obtained by         reacting hydroxy- or aminocarboxylic acids comprising or         consisting of at least one carboxylic acid selected from         2,2-dimethylolacetic acid, 2,2-dimethylolbutyric acid,         2,2-dimethylolpentanoic acid, dihydroxysuccinic acid,         α,Ω-diaminovaleric acid or mixtures thereof, preferably from         dimethylolpropionic acid or hydroxypivalic acid. -   7. Aqueous uretdione group-containing composition according to any     of the preceding aspects, characterized in that     -   the polyol (B) containing at least one hydroxyl group has an OH         content greater than 1% by weight, calculated as OH groups based         on the solids content, a molecular weight of 17 g/mol, and a         number-average molecular weight Mn of 500 to 20 000 g/mol. -   8. Aqueous uretdione dispersion according to any of the preceding     aspects, characterized in that     -   the solvent is selected from acetone, methyl ethyl ketone, ethyl         acetate, butyl acetate, xylene, solvent naphtha, such as the         commercially available Solvesso 100 or Solvesso 150, propylene         glycol mono-n-butyl ether, dipropylene glycol dimethyl ether,         methoxypropyl acetate, dibasic esters or mixtures thereof. -   9. Aqueous uretdione dispersion according to any of the preceding     aspects, characterized in that     -   the auxiliaries and additives are selected from the group         consisting of leveling agents, for example polysilicones or         acrylates, light stabilizers, for example sterically hindered         amines, catalysts, for example tin(II) 2-ethylhexanoate or         dibutyltin dilaurate, fillers, and pigments, for example         titanium dioxide, or mixtures thereof -   10. Aqueous uretdione group-containing composition according to any     of the preceding aspects, characterized in that     -   the sum of the proportions by weight of (A), (B), and (D) is 30%         to 60% by weight based on the solids content of the total         aqueous composition. -   11. A process for producing a polyurethane layer comprising the     steps of     -   i) providing an aqueous uretdione group-containing composition         according to any of aspects 1 to 10;     -   ii) applying to a substrate the mixture obtained in i);     -   iii) drying the mixture from step ii), and     -   iv) curing the mixture from step iii) by heating to from 40° C.         to 180° C. for up to 180 minutes. -   12. The process according to aspect 11, characterized in that the     aqueous uretdione group-containing composition was obtained by     mixing the uretdione group-containing curing agent (A) with the     polyol (B) containing at least one hydroxyl group in the absence of     water and subsequently dispersing the mixture with water. -   13. A polyurethane layer, in particular polyurethane film,     obtainable by a process according to aspect 11 or 12. -   14. A substrate that is coated or bonded with the polyurethane layer     according to aspect 13.

The average molecular weight is according to this invention defined as the number-average molecular weight Mn, unless explicitly stated otherwise. The Mn is determined by gel-permeation chromatography (GPC) at 23° C. in tetrahydrofuran as solvent. The measurement is carried out as described in DIN 55672-1:2016-03: “Gel permeation chromatography, Part 1—Tetrahydrofuran as eluent” (Security GPC system from PSS Polymer Service, flow rate 1.0 ml.

Unless explicitly stated otherwise, % by weight in the present invention refers to the total weight of the respective system or the total weight of the respective component. For example, a copolymer may have a content of a particular monomer that is expressed in % by weight, in which case the percent by weight values would be based on the total weight of the copolymer.

Unless explicitly stated otherwise, the expression “at least one” refers to the type of compound and not to individual molecules. For example, at least one polyol is to be understood as meaning that at least one type of polyol is present, but is present in the composition in an indeterminate number of molecules. Hence it is also possible for two or more types of polyol be present, in each case in an indeterminate number if the amounts are not defined.

In a preferred embodiment, the aqueous uretdione group-containing composition is substantially free of any other co-emulsifier (in addition to component (B)). The term “substantially free of” is according to the present invention defined as meaning that the composition contains preferably less than 1% by weight, more preferably less than 0.25% by weight, even more preferably less than 0.1% by weight, most preferably less than 0.01% by weight or no content at all of the respective compound, in each case based on the total weight of the aqueous uretdione group-containing composition.

The aqueous uretdione group-containing composition of the present invention is preferably a polyurethane-based composition.

Suitable uretdione group-containing polyisocyanates as starting compounds for component (A) are polyisocyanates that contain at least one isocyanate group and at least one uretdione group. These are prepared through the reaction of suitable starting isocyanates (a1) as described for example in WO 02/92657 A1 or WO 2004/005364 A1. In this reaction, some of the isocyanate groups are converted into uretdione groups with the aid of a catalyst, for example a triazolate or 4-dimethylaminopyridine (DMAP). Examples of isocyanates (a1) from which the uretdione-containing structural units are constructed are tetramethylene diisocyanate, cyclohexane-1,3-diisocyanate and cyclohexane-1,4-diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate (HDI), 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane (isophorone diisocyanate IPDI), dicyclohexylmethane-2,4′-diisocyanate and/or dicyclohexylmethane-4,4′-diisocyanate, tetramethylxylylene diisocyanate (TMXDI), triisocyanatononane, tolylene diisocyanate (TDI), diphenylmethane-2,4′-diisocyanate and/or diphenylmethane-4,4′-diisocyanate (MDI), triphenylmethane-4,4′-diisocyanate or naphthylene-1,5-diisocyanate, and any desired mixtures of such isocyanates. Preference is given to isophorone diisocyanate, dicyclohexylmethane-2,4′-diisocyanate and/or dicyclohexylmethane-4,4′-diisocyanate or hexamethylene diisocyanate.

In addition to the isocyanate groups and uretdione groups, component (A) may also contain isocyanurate, biuret, allophanate, urethane and/or urea structures.

The conversion of these uretdione group-bearing polyisocyanates into uretdione group-containing curing agents (A) involves the reaction of the free NCO groups of the abovementioned polyisocyanates with a polyol component (b1), optionally with the additional use of the polyol component (b2).

The polyol component (b1) preferably has a hydroxy group functionality of >2 and a molecular weight M. of 62 to 500 g/mol, preferably 62 to 400 g/mol, more preferably 62 to 300 g/mol. The polyol component (b1) preferably contains dihydric to hexahydric polyol components having a molecular weight Mn of 62 to 500 g/mol, preferably 62 to 400 g/mol, more preferably 62 to 300 g/mol. Examples of preferred polyol components (b1) are 1,4-butanediol and/or 1,3-butanediol, 1,6-hexanediol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane, polyester polyols and/or polyether polyols having an average molecular weight M. of less than or equal to 500 g/mol.

Suitable linear difunctional polyols (b2) are selected from the group consisting of polyethers, polyesters, polycaprolactone diols, and/or polycarbonates. The polyol component (b2) preferably comprises at least one diol containing ester groups and having a molecular weight Mn of 350 to 4000 g/mol, preferably of 350 to 2000 g/mol, more preferably of 350 to 1000 g/mol, This is the average molecular weight that is calculable from the hydroxyl value. The ester diols are generally mixtures in which individual constituents having a molecular weight below or above these limits may also be present in minor amounts. These are the polyester diols known per se that are constructed from diols and dicarboxylic acids.

Examples of suitable diols are 1,4-dimethylolcyclohexane, 1,4-butanediol or 1,3-butanediol, 1,6-hexanediol, neopentyl glycol, 2,2,4-trimethyl-1,3-pentanediol, trimethylolpropane and pentaerythritol, and mixtures of such diols. Examples of suitable dicarboxylic acids are aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid, cycloaliphatic dicarboxylic acids such as hexahydrophthalic acid, tetrahydrophthalic acid, endomethylenetetrahydrophthalic acid, and the anhydrides thereof, and aliphatic dicarboxylic acids, which are used with preference, for example succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, and sebacic acid or the anhydrides thereof.

Polyester diols based on adipic acid, phthalic acid, isophthalic acid, and tetrahydrophthalic acid are preferably used as component (b2). Examples of preferred diols used are 1,4-butanediol or 1,3-butanediol, 1,6-hexanediol or trimethylolpropane, and mixtures thereof.

Also preferable as component (b2) are polycaprolactone diols having an average molecular weight of 350 to 4000 g/mol, preferably of 350 to 2000 g/mol, more preferably of 350 to 1000 g/mol, that are prepared in a manner known per se starting from a diol or diol mixture of the type mentioned above, and lactones such as β-propiolactone, γ-butyrolactone, γ- and δ-valerolactone, ε-caprolactone, 3,5,5- and 3,3,5-trimethylcaprolactone or any desired mixtures of such lactones.

Particular preference is given to polycaprolactone diols that are prepared by polymerizing ε-caprolactone.

(Co)polyethers of ethylene oxide, propylene oxide, and/or tetrahydrofuran containing less than 30 mol % of ethylene oxide units may also be used as the linear polyol component (b2). Preference is given to polyethers having an average molar weight Mn of 500 to 2000 g/mol, for example polypropylene oxides or polytetrahydrofuran diols.

Also suitable as (b2) are hydroxyl-containing polycarbonates, preferably having an average molar weight Mn of 400 to 4000 g/mol, preferably of 400 to 2000 g/mol, for example hexanediol polycarbonate and polyester carbonates.

The polyol component (b2) used in the preparation of the uretdione group-containing curing agents (A) may also take the form of diols containing low-molecular-weight ester groups and having an average molecular weight, calculable from the functionality and hydroxyl value, of 134 to 349 g/mol, preferably 176 to 349 g/mol. Examples of these include the diols containing ester groups that are known per se, or mixtures of such diols, as can be prepared for example by reacting alcohols with substoichiometric amounts of dicarboxylic acids, corresponding dicarboxylic anhydrides, corresponding dicarboxylic esters of lower alcohols or lactones. Examples of suitable acids are succinic acid, adipic acid, sebacic acid, phthalic acid, isophthalic acid, phthalic anhydride, tetrahydrophthalic acid, maleic acid, maleic anhydride, dimethyl terephthalate, and bisglycol terephthalate. Examples of suitable lactones for preparing said ester diols are β-propiolactone, γ-butyrolactone, γ- and δ-valerolactone, ε-caprolactone, 3,5,5- and 3,3,5-trimethylcaprolactone or any desired mixtures of such lactones.

Amino-functional compounds may also be used in the preparation of the uretdione group-containing curing agents (A). Examples of suitable low-molecular-weight amino-functional compounds are aliphatic and cycloaliphatic amines and aminoalcohols having primary and/or secondary amino groups, for example cyclohexylamine, 2-methyl-1,5-pentanediamine, diethanolamine, monoethanolamine, propylamine, butylamine, dibutylamine, hexylamine, monoisopropanolamine, diisopropanolamine, ethylenediamine, 1,3-diaminopropane, 1,4-diaminobutane, isophoronediamine, diethylenetriamine, ethanolamine, aminoethylethanolamine, diaminocyclohexane, hexamethylenediamine, methyliminobispropylamine, iminobispropylamine, bis(aminopropyl)piperazine, aminoethylpiperazine, 1,2-diaminocyclohexane, triethylenetetramine, tetraethylenepentamine, bis(4-aminocyclohexyl)methane, bis(4-amino-3-methylcyclohexyl)methane, bis(4-amino-3,5-dimethylcyclohexyl)methane, bis(4-amino-2,3,5-trimethylcyclohexyl)methane, 1,1-bis(4-aminocyclohexyl)propane, 2,2-bis(4-aminocyclohexyl)propane, 1,1-bis (4-aminocyclohexyl) ethane, 1,1-bis(4-aminocyclohexyl)butane, 2,2-bis (4-aminocyclohexyl)butane, 1,1-bis(4-amino-3-methylcyclohexyl) ethane, 2,2-bis (4-amino-3-methylcyclohexyl)propane, 1,1-bis (4-amino-3,5-dimethylcyclohexyl)ethane, 2,2-bis (4-amino-3,5-dimethylcyclohexyl)propane, 2,2-bis (4-amino-3,5-dimethylcyclohexyl)butane, 2,4-diaminodicyclohexylmethane, 4-aminocyclohexyl-4-amino-3-methylcyclohexylmethane, 4-amino-3,5-dimethylcyclohexyl-4-amino-3-methylcyclohexylmethane, and 2-(4-aminocyclohexyl)-2-(4-amino-3-methylcyclohexyl)methane.

Solvents may optionally be used in the preparation of the uretdione group-containing curing agents (A). Suitable as solvent for the uretdione group-containing curing agents (A) are all liquid substances that do not react with other constituents, for example acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, solvent naphtha, such as the commercially available Solvesso 100 and Solvesso 150, propylene glycol mono-n-butyl ether, dipropylene glycol dimethyl ether, methoxypropyl acetate, dibasic esters or mixtures thereof.

The uretdione group-containing curing agents (A) are substantially free of ionic or nonionic, chemically bonded hydrophilizing groups. Tonically hydrophilizing groups are understood by those skilled in the art as meaning groups having the capability of forming anions or cations. Groups capable of forming anions or cations are ones that can be converted into an anionic or cationic group through chemical reaction, in particular through neutralization.

The uretdione group-containing curing agents (A) are preferably free of carboxyl group-containing polyols or diols capable of anion formation, for example dihydroxycarboxylic acids such as α,α-dialkylolalkanoic acids, in particular α,α-dimethylolalkanoic acids such as 2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, or polyhydroxy acids such as gluconic acid. In addition, the uretdione group-containing curing agents (A) are preferably free of compounds containing amino groups and capable of anion formation such as α,Ω-diaminovaleric acid or 2,4-diaminotoluenesulfonic acid. The uretdione group-containing curing agents (A) are also preferably free of sulfonic acid groups capable of anion formation.

The uretdione group-containing curing agents (A) are additionally preferably free of compounds capable of cation formation from the group consisting of tertiary amino or ammonium compounds, for example tris(hydroxyalkyl)amines, N,N′-bis(hydroxyalkyl)alkylamines, N-hydroxyalkyldialkylamines, trisaminoalkylamines, N,N′-bis(aminoalkyl)alkylamines, N-aminoalkyldialkylamines, and mixtures thereof.

The uretdione group-containing curing agents (A) are further preferably free of nonionically hydrophilizing compounds such as polyalkylene oxide polyether alcohols or polyalkylene oxide polyether amines. In particular, the uretdione group-containing curing agents (A) are preferably free of polyethylene oxide polyethers or mixed polyalkylene oxide polyethers in which 30 mol % or more of the alkylene oxide units consist of ethylene oxide units.

Preferred uretdione group-containing curing agents (A) have a free NCO content of less than 5% by weight and a content of uretdione groups of 1% to 18% by weight (calculated as C₂N₂O₂, molecular weight 84 g/mol). In addition to the uretdione groups, the curing agents (A) may also contain isocyanurate, biuret, allophanate, urethane, and/or urea structures.

The composition also comprises at least one hydroxyl-containing polyol that contains at least one chemically-bonded carboxylic acid group (component (B)).

Suitable polyols (B) may be selected from polyester polyols, polyether polyols, polyurethane ether polyols, polyurethane ester polyols, polycaprolactone polyols, polyether ester polyols, polycarbonate polyols, C₂₋₁₀ hydrocarbon containing at least two hydroxy groups or mixtures thereof, provided such polyols have at least one chemically bonded carboxylic acid group. Preference is given to suitable polyols (B) from the group consisting of polyurethane ether polyols, polyurethane ester polyols, polycaprolactone polyols or polycarbonate polyols, with particular preference given to polyurethane ester polyols (B) prepared from 5% to 80% by weight, preferably 10% to 60% by weight, of isocyanates (a1),

10% to 80% by weight, preferably 40% to 70% by weight, of polyols (b2) and/or amino-functional compounds having an average molar weight Mn of at least 400 g/mol; 2% to 15% by weight, preferably 3% to 10% by weight, of a starting component (b3) having at least one chemically bonded carboxylic acid group, 0% to 20% by weight, preferably 1-10%, of polyols (b1), 0% to 20% by weight of compounds that are monofunctional or contain active hydrogen of varying reactivity. and 0% to 20% by weight of compounds that are different than (b1), (b2), and (b3) and contain at least two groups reactive toward NCO groups.

Suitable as the starting component (b3) for the polyols (B) having at least one chemically bonded carboxylic acid group are polyols, preferably diols, containing at least one carboxylic acid group, generally 1 to 3 carboxylic acid groups, per molecule. Examples include dihydroxycarboxylic acids such as α,α-dialkylolalkanoic acids, in particular α,α-dimethylolalkanoic acids such as 2,2-dimethylolacetic acid, 2,2-dimethylolpropionic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, and also polyhydroxy acids such as gluconic acid, or aminocarboxylic acids such as α,Ω-diaminovaleric acid, and 2,4-diaminotoluenesulfonic acid. Mixtures of the compounds described above may also be used.

Particular preference is given to 2,2-dimethylolpropionic acid as the starting component (b3) for the polyols (B) having at least one chemically bonded carboxylic acid group. Alternatively, monohydroxy-functional compounds having at least one carboxylic acid group, such as hydroxypivalic acid or hydroxydecanoic acid, may also be used.

Suitable polyols (B) are polyols preferably having an OH content greater than 1% by weight (calculated as OH groups based on the solids content, molecular weight 17 g/mol) and preferably having a number-average molecular weight Mn of 500 to 20 000 g/mol, preferably of 500 to 10 000 g/mol, more preferably of 500 to 5000 g/mol.

The polyurethane resin used according to the invention is preferably produced in such a way that a non-aqueous resin precursor of the polyol (B) is mixed homogeneously in a non-aqueous system with at least one uretdione group-containing curing agent (A) based on aliphatic, (cyclo)aliphatic, araliphatic and/or aromatic polyisocyanates that contains no chemically bonded hydrophilizing groups. After this, the carboxylic acid groups present in the polyol (B) are neutralized with suitable neutralizing agents preferably to at least 50%, more preferably 80% to 120%, particularly preferably 95 to 105%, and then dispersed with deionized water. The neutralization can take place before, during or after the dispersion step. Neutralization before the addition of water is however preferred.

Examples of suitable neutralizing agents are triethylamine, dimethylaminoethanol, dimethylcyclohexylamine, triethanolamine, methyldiethanolamine, diisopropanolamine, ethyldiisopropylamine, diisopropylcyclohexylamine, N-methylmorpholine, 2-amino-2-methyl-1-propanol, ammonia or other customary neutralizing agents or neutralizing mixtures thereof. Preference is given to tertiary amines such as triethylamine and diisopropylhexylamine, and particular preference to dimethylethanolamine

In accordance with the present invention, the neutralizing agents are to be included in the group of auxiliaries and additives (D).

Suitable as solvents under (C) are all liquid substances that do not react with other constituents. Preference is given to acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, solvent naphtha, such as the commercially available Solvesso 100 and Solvesso 150, propylene glycol mono-n-butyl ether, dipropylene glycol dimethyl ether, methoxypropyl acetate, dibasic esters or mixtures thereof. The solvent used may then optionally be removed by distillation.

In accordance with the invention, additives (D) that are customary in coatings and adhesives technology, for example leveling agents such as polysilicones or acrylates, light stabilizers such as sterically hindered amines, catalysts, for example tin(II) 2-ethylhexyloctoate or dibutyltin dilaurate, or other auxiliaries such those described in EP 0 669 353, may be present in a total amount of preferably 0.05% to 5% by weight. Fillers and pigments such as titanium dioxide may be added to the aqueous composition in an amount of up to 50% by weight.

In a preferred embodiment, the aqueous uretdione group-containing composition contains or consists of

10-50% by weight, preferably 20-40% by weight, of A) based on the sum A+B 10-80% by weight, preferably 40-70% by weight, of B) based on the sum A+B 0% to 20% by weight, preferably 1% to 15% by weight, of C) based on the sum of A+B+D 0-70% by weight, preferably 2-50% by weight, of D) based on A+B+D.

EXAMPLES Raw Materials Used:

Polyester 1: an aliphatic polyester prepared from 1419 g of trimethylolpropane, 4773 g of neopentyl glycol, 3093 g of adipic acid, 4101 g of isophthalic acid, and 267 g of 1,2-propylene glycol, having an acid value of <3 mg KOH/g and an OH value of 181 mg KOH/g.

Analytical Methods Used:

All viscosity measurements were carried out using a Physica MCR 51 rheometer from Anton Paar Germany GmbH (DE) in accordance with DIN EN ISO 3219:1994-10.

NCO contents were determined titrimetrically in accordance with DIN EN ISO 11909:2007-05.

OH values were determined titrimetrically in accordance with DIN EN ISO 4629-2:2015-02.

Acid values were determined titrimetrically in accordance with DIN EN ISO 2114:2002-06.

Solids contents were determined in a circulating-air oven in accordance with DIN EN ISO 3251:2008-06, method B.

Mean particle sizes (MPS) were determined using a Zetasizer Nano from Malvern (DE) in accordance with DIN ISO 13321:2004-10.

pH determinations were carried out using a pH meter in accordance with DIN ISO 976:2008-07 in a 1:4 dilution with distilled water.

Residual monomer contents were measured in accordance with DIN EN ISO 10283 by gas chromatography with an internal standard.

Pendulum hardness was measured on a standardized coil test plate (coil coating black—CS 200570, from Heinz Zanders Priif-Blech-Logistik) in accordance with DIN EN ISO 1522:2007-04 using a Konig pendulum.

Chemical resistance was measured on a standardized coil test plate (coil coating black—CS 200570, from Heinz Zanders Priif-Blech-Logistik). A cotton pad soaked in the test substance (xylene or water) was laid on the coating surface and covered with a watch glass. After the specified contact time, the cotton pad soaked in test substance was removed and the contact site dried off and immediately examined. Softening and discoloration of the coating surface were assessed. The assessment was made in accordance with DIN EN ISO 4628-1 as follows:

0 no, i.e. no noticeable damage 1 very few areas of damage, i.e. small, just about significant number 2 a few areas of damage, i.e. small, but significant number 3 moderate number of areas of damage 4 considerable number of areas of damage 5 very many areas of damage

Unless indicated otherwise, all percentages refer to percentages by weight.

Preparation of a Uretdione Group-Containing Crosslinker (Crosslinker 1, Preparation Example)

1000 g (4.50 mol) of isophorone diisocyanate (IPDI) was successively mixed at room temperature under dry nitrogen, and with stirring, with 10 g (1%) of triisodecyl phosphite and 20 g (2%) of 4-dimethylaminopyridine (DMAP) as catalyst. After 20 h, the reaction mixture, which had an NCO content of 28.7%, corresponding to a degree of oligomerization of 21.8%, was freed of volatiles, without prior addition of a catalyst poison, with the aid of a thin-film evaporator at a temperature of 160° C. and a pressure of 0.3 mbar. This yielded a light yellow uretdione polyisocyanate having a free NCO group content of 17.0%, a calculated content of uretdione groups of 20.8%, a monomeric IPDI content of 0.4%, and a viscosity of more than 200 000 mPas.

337 g of 1,4-butanediol, 108 of 2-ethylhexanol, and 569 g of ε-caprolactone were mixed at room temperature under dry nitrogen, 0.3 g of tin(II) octoate was added, and the mixture was stirred at 160° C. for 5 h and then cooled to room temperature. To this mixture was then added, over a period of 30 min, 1850 g of the above-described uretdione group-containing polyisocyanate based on IPDI, which was warmed to 80° C. The reaction mixture was stirred at a temperature of max. 100° C. until the NCO content of the reaction mixture had fallen after 7 to 8 h to a value of 0.8%. The reaction mixture was solidified by pouring it onto a metal sheet, comminuted, and then dissolved in acetone to give a solution with a solids content of 70% by weight.

Examples 1-3 (Inventive) Example 1

TABLE 1 Weight (g) Component 1: POLYESTER 1 875 DIMETHYLOLPROPIONIC ACID 55 TIN(II) 2-ETHYLHEXANOATE 1.4 ACETONE 471 Component 2: HEXAMETHYLENE DIISOCYANATE 169 Component 3: CROSSLINKER 1 (70% in ACETONE) 458 Component 4: DIMETHYLETHANOLAMINE 36 Component 5: DIST. WATER 1384

Component 1 from table 1 was weighed into a stirring apparatus under nitrogen and homogenized for 1 h at 60° C. Component 2 was then metered in at 55° C. such that the exothermicity caused the mixture to boil under reflux. The reaction mixture was kept under reflux until the NCO content had fallen below 0.05%. The reaction mixture was then cooled to 50° C. and component 3 added and stirred in for 1 h at 50° C. Component 4 was then added and stirring continued for 30 min. Finally, component 5 was stirred in over a period of 15 min and the acetone was distilled off under reduced pressure.

This yielded a dispersion with the following properties:

Solids content 49.8% by weight Acid value (100%) 20 mg KOH/g OH content (100%, calculated) 1.9% by weight Mean particle size 143 nm Viscosity 640 mPas pH 7.8

The dispersion remained stable for 14 months at 23° C.

Example 2

Example 2 was prepared in the same way as example 1, except that 718 g of the crosslinker 1 solution and 38 g of dimethylethanolamine were used. The dispersion obtained has the following properties:

Solids content 42.6% by weight Acid value (100%) 18 mg KOH/g OH content (100%, calculated) 1.7% by weight Mean particle size 180 nm Viscosity 850 mPas pH 8.0

The dispersion remained stable for 14 months at 23° C.

Example 3

Example 3 was prepared in the same way as example 1, except that the amounts shown below in table 2 were used.

TABLE 2 Weight (g) Component 1: POLYESTER 1 759 DIMETHYLOLPROPIONIC ACID 60 TIN(II) 2-ETHYLHEXANOATE 1.3 ACETONE 667 Component 2: HEXAMETHYLENE DIISOCYANATE 181 Component 3: CROSSLINKER 1 (70% in ACETONE) 1043 Component 4: DIMETHYLETHANOLAMINE 42 Component 5: DIST. WATER 1690

The dispersion obtained has the following properties:

Solids content 40.0% by weight Acid value (100%) 17 mg KOH/g OH content (100%, calculated) 1.2% by weight Mean particle size 261 nm Viscosity 320 mPas pH 7.6

The dispersion remained stable for 10 months at 23° C.

Example 4 (Comparative)

1000 g (4.50 mol) of isophorone diisocyanate (IPDI) was successively mixed at room temperature under dry nitrogen, and with stirring, with 10 g (1%) of triisodecyl phosphite and 20 g (2%) of 4-dimethylaminopyridine (DMAP) as catalyst. After 20 h, the reaction mixture, which had an NCO content of 28.7%, corresponding to a degree of oligomerization of 21.8%, was freed of volatiles, without prior addition of a catalyst poison, with the aid of a thin-film evaporator at a temperature of 160° C. and a pressure of 0.3 mbar.

A light yellow uretdione polyisocyanate having a free NCO group content of 17.0% and a viscosity of more than 200 000 mPas was obtained.

219 g of the above-described uretdione group-containing polyisocyanate, based on IPDI and having a free isocyanate group content of 17.0% and a calculated uretdione group content of 20.8%, was under dry nitrogen to 80° C. was weighed into a stirring apparatus under nitrogen and dissolved in 849 g of acetone at room temperature. 22.9 g of dimethylolpropionic acid and 2.11 g of tin(II) 2-ethylhexanoate were then metered into the homogeneous solution such that the exothermicity caused it to boil under reflux. The reaction mixture was kept under reflux until an NCO content of 2.2% was reached. 265.9 g of polyester 1 was then added and the reaction mixture was stirred under reflux until the NCO content of the reaction mixture had fallen to a value below 0.1%. cooled to 50° C. After cooling to 23° C., 16.8 g of dimethylethanolamine was added to the reaction mixture and stirring was continued for 30 min. Finally, 1451 g of distilled water was stirred in over a period of 15 min and the acetone was distilled off under reduced pressure. This yielded a dispersion with the following properties:

Solids content 37.62% by weight Mean particle size 91 nm Viscosity 30 mPas pH 8.0

After 6 months at 23° C. this dispersion had developed sediment and after 6 days of storage at 40° C. it had gelled completely.

Tests of Coating Properties Examples 5-7 (Inventive)

Clear coatings were produced from the following compositions (all weights are in g):

TABLE 3 Example 5 6 7 Composition from example 1 10.00 Composition from example 2 10.00 Composition from example 3 10.00

The dispersions were mixed in a SpeedMixer at 2000 rpm for 1 minute and then applied to a metal coil test plate in a layer thickness of 180 μm (wet) using a coating blade. The plates with the applied wet coatings were flashed off for 5 min at room temperature and then baked for 30 min at 180° C. and stored for 4 days at room temperature. The performance of the stored films was assessed (table 4).

TABLE 4 Example 5 6 7 Appearance of the coating satisfactory satisfactory satisfactory (visual examination) Film thickness (dry, μ) 50 60 50 Pendulum hardness (s) 95 145 200 Resistance to xylene 3 3 3 (5 minutes) Deionized water (1 hour) 1 1 0

As can be seen from table 4, the uretdione-containing dispersions of the invention afford hard and resistant coatings. 

1. An aqueous uretdione group-containing compositions comprising; (A) at least one uretdione group-containing curing agent based on aliphatic, cycloaliphatic, araliphatic or aromatic polyisocyanates that contains no chemically-bonded hydrophilizing groups; (B) at least one hydroxyl-containing polyol that contains at least one chemically-bonded carboxylic acid group; (C) optionally, solvents; and (D) optionally, auxiliaries and additives; wherein the quantitative ratio of components (A) and (B) is such that the molar ratio of the NCO groups of the curing agent (A) present as uretdione to NCO-reactive groups of the polyol (B) is 3.0:0.5 to 0.5:3.0 and wherein A and B are present as a mixture.
 2. The composition as claimed in claim 1, wherein the at least one uretdione group-containing curing agent (A) is obtained by reacting monomeric isocyanates comprising at least one monomeric isocyanate selected from the group consisting of tetramethylene diisocyanate, cyclohexane-1,3-diisocyanate, cyclohexane-1,4-diisocyanate, pentamethylene diisocyanate, hexamethylene diisocyanate-, 1-isocyanato-3,3,5-trimethyl-5-isocyanatomethylcyclohexane, dicyclohexylmethane-2,4′-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, tetramethylxylylene diisocyanate, triisocyanatononane, tolylene diisocyanate, diphenylmethane-2,4′-diisocyanate, diphenylmethane-4,4′-diisocyanate, triphenylmethane-4,4′-diisocyanate, naphthylene-1,5-diisocyanate, and mixtures thereof.
 3. The composition as claimed in claim 1, wherein hydroxyl-containing monomers or polymers are used as starting materials for the at least one uretdione group-containing curing agent (A).
 4. The composition as claimed in claim 1, wherein the at least one uretdione group-containing curing agent (A) has a free NCO content of less than 5% by weight and a content of uretdione groups of 1% to 18% by weight (calculated as C₂N₂O₂, molecular weight 84 g/mol).
 5. The composition as claimed in claim 1, wherein the aqueous composition has an acid value of 1 to 100 mg KOH/g.
 6. The composition as claimed in claim 1, wherein the at least one hydroxyl-containing polyol (B) is obtained by reacting hydroxy- or aminocarboxylic acids comprising at least one carboxylic acid selected from the group consisting of 2,2-dimethylolacetic acid, 2,2-dimethylolbutyric acid, 2,2-dimethylolpentanoic acid, dihydroxysuccinic acid, α,Ω-diaminovaleric acid, and mixtures thereof.
 7. The composition as claimed in claim 1, wherein the polyol (B) containing at least one hydroxyl group has an OH content greater than 1% by weight, calculated as OH groups based on the solids content, a molecular weight of 17 g/mol, and a number-average molecular weight Mn of 500 to 20 000 g/mol.
 8. The composition as claimed in claim 1, wherein the solvent is selected from the group consisting of acetone, methyl ethyl ketone, ethyl acetate, butyl acetate, xylene, solvent naphtha, propylene glycol mono-n-butyl ether, dipropylene glycol dimethyl ether, methoxypropyl acetate, dibasic esters, and mixtures thereof.
 9. The composition as claimed in claim 1, wherein the auxiliaries and additives are selected from the group consisting of leveling agents, light stabilizers, catalysts, fillers, and pigments, and mixtures thereof.
 10. The composition as claimed in claim 1, wherein the sum of the proportions by weight of (A), (B), and (D) is 30% to 60% by weight based on the solids content of the total aqueous composition.
 11. A process for producing a polyurethane layer comprising the steps of i) providing an aqueous uretdione group-containing composition as claimed in claim 1; ii) applying to a substrate the composition obtained in i) to produce a mixture; iii) drying the mixture from step ii), and iv) curing the mixture from step iii) by heating to from 40° C. to 180° C. for up to 180 minutes.
 12. The process as claimed in claim 11, wherein the aqueous uretdione group-containing composition is obtained by mixing the uretdione group-containing curing agent (A) with the polyol (B) containing at least one hydroxyl group in the absence of water to obtain a mixture, and subsequently dispersing the mixture with water.
 13. A polyurethane layer obtained by the process as claimed in claim
 11. 14. A substrate coated or bonded with the polyurethane layer as claimed in claim
 13. 